This invention relates to the use of an ion exchange resin to remove impurities such as calcium from a chlorate mother liquor. Specifically, it relates to the use of a cationic chelating ion exchange resin to remove as much calcium from the recycled mother liquor as is added in the feed.
Sodium chlorate crystals can be made by electrolyzing a sodium chloride brine stream in an electrolytic cell to produce a solution of sodium chlorate. After concentration, if necessary, the solution is cooled to precipitate the sodium chlorate crystals. In order to increase the concentration of sodium chlorate, it is desirable to recycle the mother liquor from the crystallizer to the cells.
The brine used to make sodium chlorate normally contains calcium. The calcium concentration in the brine must be kept low in order for the cell to operate efficiently. Although most of the calcium in the brine can be removed by precipitation with sodium carbonate, about 1/2 to about 5 parts by weight per million of solution (ppm) of calcium can remain in the brine. Since only a small amount of that calcium is removed with the sodium chlorate crystals, the concentration of calcium and other impurities in the electrolytic system would quickly build up as the mother liquor from the crystallizer is recycled.
The impurities in the system can be removed by dumping the system about every six months and washing the cells, but this represents a loss of a substantial amount of production time and cost for tankage and liquor cleanup. Removal by conventional ion exchange is also possible but is very expensive.